In the midst of the world’s sixth mass extinction, it comes as a bit of a shock to discover that the first marine fish to be officially listed as extinct by the IUCN, in the modern era, was only declared so last year. The fish in question is known as a smooth handfish (Sympterichthys unipennis) and was last sighted over 200 years ago.

Handfish

Handfish are an interesting group of shallow, bottom-dwelling fish which ‘walk’ along the ocean floor on modified hand-like pectoral fins. They are closely related to deep-sea anglerfish and are often described as a ‘missing-link’ type creature. They are very rare and have been identified as the most threatened marine bony fish family. 7 of the 14 (now 13) are listed as endangered or even critically endangered and only 4 species have recorded sightings since the turn of the century.

Smooth Handfish

The smooth handfish is known only from a single specimen collected in 1802 by the French biologist François Péron during a scientific research expedition to southern Australia. The expedition was led by Captain Nicolas Baudin from 1800 to 1804 and was the first scientific exploration of the region’s marine life. It is likely simple dip nets were used to capture shallow-living species for identification and collection. Current ichthyological researchers, Last and Gledhill (2009), believe the D’Entrecasteaux Channel in southeastern Tasmania is where the specimen was collected, based on where other samples were collected during the expedition, the type of gear available over 200 years ago and the distribution of species in the same family.

Even though only one specimen is known to science, it is likely that this species was fairly common at the time of discovery and was one of the first Australian species described in Europe. Today, the holotype specimen is housed at the Museum National d’Histoire Naturelle in Paris and a thorough taxonomic revision of all handfish species has confirmed that this individual is morphometrically and meristically distinct from other known handfish.

Habitat and Ecology

As very little is known about this species, much of its ecology is inferred from other congeneric species found in southeastern Tasmania. Typically, handfish in this area inhabit rocky and sandy benthic environments. Small clusters of large eggs are laid by the female against a vertical substrate and attached by filaments. The eggs are watched over until they hatch.

Vulnerability To Extinction

As handfish do not have a pelagic (or open ocean) larval stage, the species have very limited dispersal abilities and populations often become isolated from each other.  This, together with a relatively low reproductive rate, makes handfish particularly predisposed to population declines as they are slow to recover from disturbances and susceptible to inbreeding. Isolation can also lead to a loss of genetic diversity as there is little to no gene flow between populations. Genetic diversity is becoming increasingly important in wild populations as the effects of climate change become more prevalent. Populations with high levels of genetic diversity have a higher adaptation potential than populations with low genetic diversity because more variation exists within the population and certain characteristics may allow some individuals to be more successful than others in adverse environmental conditions.

Threats

Although the exact cause of extinction may always remain a mystery, researchers are able to infer the likely causes of the smooth handfish’s extinction based on the threats currently experienced by other species of handfish, as well as the characteristics which make handfish more susceptible to extinction than other types of fish. 

Large-scale population declines have been recently recorded in similar species to the smooth handfish, such as the Red Handfish (Thymichthys politus), Spotted Handfish (Brachionichthys hirsutus) and Ziebell’s Handfish (Brachiopsilus ziebelli). These severe population declines have been linked to anthropogenic impacts such as water pollution, siltation, spawning sites destruction, the spread of invasive species and habitat loss and degradation. 

In particular, large scallop and oyster fisheries were known to have operated in the late 19th century and dredged every part of the D’Entrecasteaux Channel. This is likely to have contributed to the extinction of the smooth handfish – both indirectly from destruction of the benthic environment and also from direct mortality as the result of being bycatch. 

Why Has It Only Been Listed As Extinct Now?

There are many challenges involved in declaring a marine species extinct – as it is very challenging to prove that something isn’t ‘there’, when ‘there’ is the entire ocean. Marine fish species typically have very wide geographic ranges and also inhabit variable depths which makes them difficult to detect in the first place. Handfish, however, are shallow water fish that have a very restricted range which makes it easier to monitor populations and estimate the numbers of individuals present – so it is unsurprising that they are among the first marine species to be listed as extinct. In addition, many scientific diving expeditions have been conducted in the area – specifically targeting the different species of handfish, as part of the Handfish Conservation Project. Many diving trips have also been undertaken in the area to monitor the scallop population numbers following the collapse of the fisheries in the 1960s. Because of the extensive number of surveys carried out in the smooth handfish’s restricted habitat over many years without any sightings recorded, the researchers are able to reasonably conclude that the species is extinct. However, this is not possible for all species and detection challenges are thought to preclude many fish species from being listed as extinct. It is very likely that many other species of fish have disappeared from our oceans already and more are likely to follow as anthropogenic pressures on the marine environment increase and climate change continues to impact oceanic conditions. While the smooth handfish may claim the title of the first marine fish to be officially declared extinct, it is unlikely to be the last unless we commit to reducing our impact on the marine environment and responsibly manage how we harvest food from the ocean.